The present invention relates in general to data storage systems such as disk drives, and it particularly relates to a thin film read/write head for use in such data storage systems. More specifically, the present invention relates to a thin film, inductive tape read/write head with a spin-dependent tunneling sensor with a low resistance metal oxide tunnel barrier for increased density read sensors at high data transfer rate.
In a conventional magnetic storage system, a thin film magnetic head includes an inductive read/write element mounted on a slider. The magnetic head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying, height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
A magnetic head typically includes a thin film read transducer formed in a read gap between two shields. The transducer can be a spin-dependent tunneling sensor (SDTS) which is comprised of two ferromagnetic layers separated by a thin insulating tunnel barrier and is based on the phenomenon of spin-polarized electron tunneling. One of the ferromagnetic layers has a higher saturation field in one direction of an applied magnetic field, typically due to its higher coercivity than the other ferromagnetic layer. The insulating tunnel barrier is thin enough that quantum mechanical tunneling occurs between the ferromagnetic layers. The tunneling phenomenon is electron-spin dependent, making the magnetic response of the spin-dependent tunneling sensor a function of the relative orientations and spin polarizations of the two ferromagnetic layers.
The state of the spin-dependent tunneling sensor is determined by measuring the resistance of the spin-dependent tunneling sensor when a sense current is passed perpendicularly through the spin-dependent tunneling sensor from one ferromagnetic layer to the other.
The probability of tunneling of charge carriers across the insulating tunnel barrier depends on the relative alignment of the magnetic moments (magnetization directions) of the two ferromagnetic layers. The tunneling current is spin polarized, which means that the electrical current passing from one of the ferromagnetic layers, for example, a layer whose magnetic moment is fixed or prevented from rotation, is predominantly composed of electrons of one spin type (spin up or spin down, depending on the orientation of the magnetic moment of the ferromagnetic layer).
The degree of spin polarization of the tunneling current is determined by the electronic band structure of the magnetic material comprising the ferromagnetic layer at the interface of the ferromagnetic layer with the tunnel barrier layer. The first ferromagnetic layer thus acts as a spin filter. The probability of tunneling of the charge carriers depends on the availability of electronic states of the same spin polarization as the spin polarization of the electrical current in the second ferromagnetic layer.
Usually, when the magnetic moment of the second ferromagnetic layer is parallel to the magnetic moment of the first ferromagnetic layer, there are more available electronic states than when the magnetic moment of the second ferromagnetic layer is aligned antiparallel to that of the first ferromagnetic layer. Thus, the tunneling probability of the charge carriers is highest when the magnetic moments of both layers are parallel, and is lowest when the magnetic moments are antiparallel. When the moments are arranged neither parallel nor antiparallel, the tunneling probability takes an intermediate value.
It has been recognized that the electrical resistance of the spin-dependent tunneling sensor depends on the spin polarization of the electrical current and the electronic states in both of the ferromagnetic layers. As a result, the two possible magnetization directions of the ferromagnetic layer whose magnetization direction is not fixed uniquely define two possible bit states (0 or 1) of the spin-dependent tunneling sensor.
A magnetoresistive (MR) sensor in a read head detects magnetic field signals through the resistance changes of a read element, fabricated of a magnetic material, as a function of the strength and direction of magnetic flux being sensed by the read element. The conventional MR sensor, such as that used as a MR read head for reading data in magnetic recording disk drives, operates on the basis of the anisotropic magnetoresistive (AMR) effect of the bulk magnetic material, which is typically permalloy (Ni81 Fe19). A component of the read element resistance varies as the square of the cosine of the angle between the magnetization direction in the read element and the direction of sense current through the read element. Recorded data can be read from a magnetic medium, such as the disk in a disk drive, because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the read element, which in turn causes a change in resistance of the read element and a corresponding change in the sensed current or voltage.
The use of a spin-dependent tunneling sensor as a MR read head and in other applications is described in the following publications:
U.S. Pat. No. 6,097,579 to Gill;
U.S. Pat. No. 6,094,428 to Bruckert, et al.;
U.S. Pat. No. 6,088,195 to Kamiguchi, et al.;
U.S. Pat. No. 6,005,753 to Fontana, Jr., et al.;
U.S. Pat. No. 5,991,125 to Iwasaki, et al.;
U.S. Pat. No. 5,966,012 to Parkin;
U.S. Pat. No. 5,923,503 to Sato, et al.;
U.S. Pat. No. 5,901,018 to Fontana, Jr., et al.;
U.S. Pat. No. 5,898,547 to Fontana, Jr., et al.;
U.S. Pat. No. 5,748,416 to Tobise, et al.;
U.S. Pat. No. 5,739,990 to Ravipati, et al.;
U.S. Pat. No. 5,729,410 to Fontana, Jr., et al.;
U.S. Pat. No. 5,708,358 to Ravipati; and
U.S. Pat. No. 5,390,061 to Nakatani, et al.
One of the problems with such spin-dependent tunneling sensors is that as the areal density in magnetic recording exceeds 60 Gigabit/in2, read sensors with relatively higher sensitivity are required. The spin dependent tunneling sensor is a very strong candidate for high-density magnetic recording read sensors because of its high magnetoresistance ratio. However, current spin-dependent tunneling sensors suffer from low data transfer rate because the combination of the high sensor resistance and the capacitance of the recording system.
Therefore, it would be desirable to provide a read head sensor that utilizes a low resistance spin-dependent tunneling sensor for increased data transfer rate.
One, aspect of the present invention is to satisfy this long felt and still unsatisfied need. According to the present invention, the read head includes a spin-dependent tunneling sensor composed of a new low resistance metal oxide tunneling barrier material, such as chromium oxide (CrxOy) or niobium oxide (NbOz).
The chromium oxide ((CrxOy) can be, for example: Cr3O4, Cr2O3, CrO2, CrO3, Cr5O12, Cr6O15, other stoichiometry, or any combination thereof. The niobium oxide (NbOz) can be, for example: NbO, NbO2, Nb2O5, Nb2O3, Nb12O29, Nb11O27, other stoichiometry, or any combination thereof.
The chromium oxides and the niobium oxides provide a very low sensor resistance with an acceptable magnetoresistance ratio. The use of spin-dependent tunneling sensors with the appropriate composition for the metal oxide barrier will enable the fabrication of high density read sensors, and thus read heads with high data transfer rate.